Initial workflow, refs #1

Author: simonw

.github/workflows/stable-docs.yml

@@ -0,0 +1,50 @@
+name: Update Stable Docs
+
+on:
+  release:
+    types: [published]
+  push:
+    branches:
+      - main
+
+permissions:
+  contents: write
+
+jobs:
+  update_stable_docs:
+    runs-on: ubuntu-latest
+    steps:
+    - name: Checkout repository
+      uses: actions/checkout@v3
+
+    - name: Set up Git user
+      run: |
+        git config user.name "Automated"
+        git config user.email "[email protected]"
+
+    - name: Check if stable-docs branch exists
+      run: |
+        if ! git rev-parse --verify stable-docs > /dev/null 2>&1; then
+          git checkout -b stable-docs
+          git push -u origin stable-docs
+        fi
+
+    - name: Handle Release
+      if: github.event_name == 'release'
+      run: |
+        git fetch --all
+        git checkout stable-docs
+        git reset --hard ${GITHUB_REF#refs/tags/}
+        git push origin stable-docs --force
+
+    - name: Handle Commit to Main
+      if: contains(github.event.head_commit.message, '!stable-docs')
+      run: |
+        git fetch --all
+        git diff-tree --no-commit-id --name-only -r ${{ github.sha }} | grep '^docs/' > changes.txt
+        if [[ -s changes.txt ]]; then
+          git checkout stable-docs
+          git checkout ${{ github.sha }} -- $(cat changes.txt)
+          git commit -m "Cherry-picked docs changes from ${{ github.sha }}"
+          git push origin stable-docs
+        fi